A classical pianist’s night at the opera turned into a nightmare at the 24th Precinct after she misplaced her ticket while attending a production of “Hamlet” at the Met.

In papers filed in Manhattan Supreme Court, Aviva Aranovich says a hotheaded cop escorted her out of the storied opera house by smashing her head into the railing and letting her fall down a marble stairway – and then slammed the door of his patrol car on her ankle.

Aranovich’s Wagnerian hell didn’t end there – the officer then repeatedly smacked her on the head at the precinct and denied her medical attention before two other officers took her to the hospital, where she was diagnosed with a concussion, the suit says.

Now the petite lady is singing with a lawsuit against the city and cops over the “brutal police conduct” and “excessive force.”

A lawyer for the city, Fay Leousis, said they hadn’t yet seen the legal papers, but when they do “we will review the matter thoroughly.”

Aranovich, a vice-president at Halstead Property who’s also a Juilliard-trained pianist, said the incident took place last March 16, after she’d accidentally given her ticket to a friend and couldn’t find her seat, the suit says. An usher demanded she leave, and when she complained to officer Fernando Grace, he smashed her into a railing and arrested her.

When she was finally released from police custody 18 hours later, she discovered the $600 she’d had on her at the time of her arrest was whittled down to $100. The criminal charges were later dropped, the suit says.

The NYPD had a drastically different version of events.

They said they’d been summoned to Lincoln Center by security personnel, and the woman “became belligerent.”

“She struggled with the officers, and contrary to her claims, injured her ankle in kicking out the rear passenger fly window,” said police spokesman Paul Browne. He said she refused EMS medical assistance at the precinct, and was taken to Bellevue Hospital for psychiatric observation. Her abuse claim was investigated and “the officer was exonerated,” Browne said. Internal Affairs also knocked down her claim that she was short-changed, he said.